Method for making an electric motor stator

ABSTRACT

A technique for making a stator for an electric motor or similar machine includes disposing a plurality of concentric coils in a stator core such that leads exit both ends of the stator core. The coils are disposed in accordance with a winding pattern that is particularly suited for making four-pole, three-phase machines. Certain of the coils are disposed singularly within core slots, while other coils share slots with coils of other winding groups. The coils may be inserted by machine, and in several layers by rotating the stator core between each layer insertion.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of electric motorsand similar machines. More particularly, the invention relates to anovel technique for making a stator for an electric motor or similarmachine.

In the field of electric motors, generators, dynamos, and similarmachines, a wide variety of configurations have been proposed and arepresently in use. Most such machines employ a stator which surrounds arotor. The stator and rotor may have various designs and electricalconfigurations depending upon the type of application, the environmentin which they are used, the available power, and other such factors. Acommon type of electrical motor, for example, is the induction motorused throughout industry and in many varied applications. Inductionmotors typically employ a stator including a core in which a pluralityof windings are installed. Other types of electrical machines usesomewhat similar stators, with rotor designs varying from permanentmagnet rotors, wound rotors, brush and brushless rotors, and so forth.

In the field of stator design, many varied approaches have beenproposed. For example, conventional stators are commonly manufacturedbased upon a core having a series of radially-disposed slots. The slotsare designed to receive the stator coils. Each slot is typicallyinsulated by a liner, and the coils are installed in the slots withleads exiting an end of the stator. The leads are interconnected ingroups and channeled within the motor housing to an exit point forconnection to a source of power.

The particular arrangement of coils within a stator defines the speedand electrical machine type. For example, coils in induction motors arewired together in groups to define poles. The synchronous speed of themotor is, then, defined by the number of poles and the frequency of thepower applied to the stator. Moreover, the groupings of coils willdefine whether the machine is suitable for single-phase power orthree-phase power. A corresponding number of slots is provided in thestator core to receive the desired number of coils for the particularmotor configuration.

Even for motors having similar synchronous speeds, power ratings, and soforth, a wide variety of winding patterns are presently in use. Thewinding patterns may be grouped, generally, into classes includinglapped designs and concentric designs. In lapped designs, one leg orside of a coil is installed in a base position in a slot, while theother leg or side of the coil is installed in a position over adifferent coil. The coils thus must “lap” over one another at ends ofthe stator core. In concentric designs, on the other hand, coilsinstalled in a base position are placed in the base position for bothlegs or sides of the coil. Thus, certain coils can be fully installedprior to installation of coils which will overlie the installed coils.Thus, the coils do not lap, but are concentric to one another, at leastwithin certain groups. Significant advantages flow from concentric coildesigns. For example, the coils can be preformed and installed byspecially-adapted machines. In lap designs, human operators typicallyinstall the coils within the stator core due to the complexity ofinstalling coil legs in base and overlying positions within the statorcore.

Despite the advantages of concentric winding designs, there is stillsignificant need for improved designs. For example, existing statordesigns typically provide for exiting leads of the stator windings froma single end of the stator core only. Where such leads become bulky,particularly where higher numbers of coil groups are employed or forhigher power or voltage applications, the available space within themotor housing may significantly limit or even make impossible theinstallation of the coils. Larger motor frame sizes would thus be neededfor particular power ratings due to the presence of the coil leadswithin the end bracket of the motor.

There is, at present, a significant need for an improved motor designbased upon a concentric pattern which reduces the congestion at ends ofthe motor due to exiting leads. There is also a need for a technique forwinding and making a motor stator which accommodates machine winding ofconcentric coils in such new patterns. There is a particular need for amethod for making four-pole motor stator for use in applicationsrequiring such motors, and, still more particularly, for three-phaserated four-pole motors having concentric winding patterns.

SUMMARY OF THE INVENTION

The present invention provides a novel technique for winding a motorstator and for building a motor based upon the stator designed torespond to such needs. The technique is based upon concentricallywinding of the stator such that coils can be preformed and installed bymachine. The technique may be used with a wide variety of stator coredesigns, including cores having 72 slots, 60 slots, 48 slots, and 30slots. In each case, the number of coils per group will vary, as may thedistribution of the coils within the core. In accordance with aspects ofthe present technique, certain slots receive a single coil, while otherslots receive a pair of coils. In either case, however, the coils areconcentric such that straightforward installation is afforded. Thetechnique, in particular, provides a novel winding arrangement for afour-pole, three-phase motor having excellent performancecharacteristics while securing the benefits of concentric winding.

The technique is specifically adapted to improve the use of internalspace within the motor by leads exiting both ends of the stator core. Ina preferred arrangement, half of the leads exits a first end of thestator core, while a second half of the leads exits the opposite end.The coil groups may be installed through the first end and through thesecond end to provide the proper exiting of the coil leads. In apreferred process, the stator core receives a first set of coils throughthe first end, is rotated, and receives a second set of coils throughthe second end. Where desired, further rotation of the stator core isperformed to install further sets of coils. In a present embodiment, thestator core is rotated three times, with four sets of coils beingsequentially installed in the stator core. Because the stator core isrotated about its central axis (transverse to its longitudinal axis),the insertion of the coils does not entail any offset of the stator coreor the insertion machinery.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages and features of the invention willbecome apparent upon reading the following detailed description and uponreference to the drawings in which:

FIG. 1 is a diagrammatical representation of an electric motor includinga stator configured in accordance with aspects of the present technique;

FIG. 2 is a diagrammatical representation of a stator of the typeincluded in the motor of FIG. 1;

FIG. 3 is a sectional view through a portion of a stator core havingcoils both filling slots and shared with slots in accordance withaspects of the present technique;

FIG. 4 is a diagrammatical representation of a 72-slot stator core woundin accordance with aspects of the present technique to provideconcentric winding of a four-pole, three-phase motor;

FIG. 5 is a diagrammatical representation of slot locations for thecoils of the stator illustrated in FIG. 4;

FIG. 6 is a flow chart illustrating exemplary steps in a process formanufacturing the stator of FIGS. 4 and 5;

FIG. 7 is a diagrammatical representation of the processing steps andpositions of the stator during the manufacturing process summarized inFIG. 6;

FIG. 8 is a flow chart illustrating exemplary steps in an alternativeprocess for manufacturing a stator core of the type illustrated in FIGS.4 and 5;

FIG. 9 is a diagrammatical representation of positions of the statorcore during the process of FIG. 8; and

FIG. 10 is a diagrammatical representation of further alternativeembodiment in which coils are installed without rotation of the core.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Turning now to the drawings and referring first to FIG. 1, adiagrammatical representation of an electric motor 10 including a statorconstructed in accordance with the aspects of the present technique isillustrated. The motor 10 may be of any desired type, rating, and style.In present embodiments, motor 10 is an induction motor designed tooperate on 3-phase alternating current. The specific voltage and currentratings of the motor may, of course, vary depending upon the applicationand design. The motor incorporates a stator 12 designed and constructedas described in greater detail below. Stator 12 is supported in ahousing 14 which is closed on either end by an end bell or bracket 16. Ashaft and rotating assembly, indicated generally at reference numeral18, is supported within the stator 12 for rotation. Leads 20 from thestator 12 are channeled around ends of the stator in passageways 24adjacent to end brackets 16. The leads exit the housing 14 at apassageway or conduit opening 22. In a final motor application, theopening 22 may be covered by a conduit box (not shown) for terminatingthe leads. It should be noted that, in addition to various voltage,power, current and other specifications, motor 10 may include anysuitable housing style, including open, TEFC, drip-proof,explosion-proof, and so forth.

As illustrated generally in FIG. 2, stator 12 is fabricated as aseparate assembly prior to mounting within housing 14 of the motor. Thestator consists of a stator core 26 which is made of a ferromagneticmaterial, such as assembled steel laminate plates. The core 26 has twoopposite axial ends 28 and 30. As described in greater detail below,sets of leads 32 and 34 of the coils within the stator core exit bothends, end 28 and end 30 respectively, to facilitate channeling of theleads within the motor housing and connection of the leads to formgroups and poles.

The technique described herein for construction of motor 10 and stator26 may be adapted for various motor configurations. However, thetechnique is particularly well-suited to construction of four-pole,three-phase motors. The technique described below is based upon a statorhaving 72 radial slots disposed about the interior of core 26. As willbe appreciated by those skilled in the art, however, the technique maybe adapted to stators having different numbers of slots, such as 60slots, 48 slots, or 36 slots. In general, the technique permits machineinstallation of the stator windings such that leads 32 and 34 exit bothends 28 and 30 of the stator core. The windings or coils installedwithin the stator core are configured as concentric coils and may beinstalled through both ends of the stator core so as to facilitateexiting of the leads through the end by which the windings areinstalled. Exemplary processes for installation of the coils aredescribed in greater detail below.

FIG. 3 illustrates a partial section through stator core 26 with severalcoils installed. The coils are installed within slots 36 formed aboutthe inner periphery of core 26. Each slot extends radially from anopening 38 at the inner periphery of core 26, to a base 40 locatedradially toward the outer periphery of the core. The slots extendaxially between the ends of the stator core (see ends 28 and 30 in FIG.2). A liner 42, which may be made of any conventional insulating andlining material, is wrapped around the inner wall of each slot 36.Individual coils, then, are installed within slots 36 through openings38. As described in greater detail below, certain of the coils of thestator are installed singularly within the slots, while other coils areinstalled so as to share a slot with a coil of a different group. In apresent embodiment, the coils which are installed singularly within theslots have a larger cross-sectional area than the coils intended toshare slots. Thus, as illustrated in FIG. 3, certain coils 44 arepositioned within individual slots, while other coils 46 and 48 arepositioned together within individual slots. Where coils are positionedso as to share slots, an insulator 50 is provided between the coils. Itshould be noted that, as described more fully below, in the concentricwinding technique described herein, where a coil is installed with asecond coil in a shared slot, the coil is positioned either in a baseposition, as are coils 46 in FIG. 3, or in a top position, as are coils48 in FIG. 3. A coil disposed in a base position in one slot will bedisposed in a base position in another slot of the core. Similarly, acoil disposed in a top position of a shared slot will be positioned in atop position of a different shared slot of the core. Thus, machineinstallation of the coils is greatly facilitated by allowing coils to befully installed (i.e., based-positioned coils) prior to installation ofsubsequent coils (i.e., top-positioned coils). Finally, it should benoted that the coils may be of any appropriate style and type, includingsolid conductor bars, conductor bundles or cables, and so forth.

As mentioned above, the windings or coils of the stator are installed soas to provide leads exiting both ends of the stator core. FIG. 4 is aschematic representation of the positioning and routing of the coils andleads in the stator core. As shown in FIG. 4, the stator core 26 in anexemplary embodiment includes 72 radially-disposed, axially-extendingslots. Coils are installed within the stator core to define the poles,and groups of coils. As will be appreciated by those skilled in the art,the number of phases, poles and groups will depend upon the particularmotor design. However, the number of poles, in the illustratedembodiment four poles, will define the synchronous speed of the motor inconjunction with the frequency of the alternating current applied to it.The present design may, of course, be used with conventional inverterdrives, such that the speed may be regulated by regulation of thefrequency of the applied current. The number of groups, and theirinterconnection, may be varied depending upon whether the coils areassociated in wye or delta configurations.

The stator 12 illustrated in FIG. 4 includes coils for three phases,referred to herein as phases A, B and C. Moreover, the stator includescoils for four groups within each phase, thereby defining a three-polemachine. The groups are installed in four layers or sets, as describedmore fully below. Each group of coils includes four individual coils.

As shown in FIG. 4, phase A includes coils 52, while phase B includescoils 54 and phase C includes coils 56. Each phase includes four coilsgroups. Coils groups for phase A only are indicated separately in FIG. 4for the sake of clarity. Thus, phase A includes groups 58, 60, 62 and64. In the diagrammatical illustration of FIG. 4, the groups areillustrated as having four separate coils. Coils only for group 58 areindicated separately in FIG. 4 for the sake of clarity. Thus, group 58includes coils 66, 68, 70 and 72.

Leads for the individual coils exit both ends of the stator core 26. Inthe embodiment illustrated in FIG. 4, for example, leads for groups 58and 62 exit a first end of the stator core while leads of groups 60 and64 exit in opposite end. In the illustration of FIG. 4, leads exiting afirst end are illustrated radially outside the stator core, while leadsexiting the opposite end or illustrated radially within the stator core.It will be noted that a certain of the coils shown in FIG. 4 aredisposed singularly within the slots, while other coils share slots.Thus, coils 66 and 68 are positioned within non-shared slots 74, whilecoils 70 and 72 are positioned within shared slots 76 (sharingindividual slots with coils of group 54 exiting an opposite end of thestator core).

The particular winding pattern illustrated in FIG. 4 is depicteddiagrammatically in FIG. 5. As shown in FIG. 5, the stator core includesslots 36 extending about its inner periphery. In the illustratedembodiment, 72 such slots are provided. In the illustration of FIG. 5,individual coil groups are identified by the phase and group numbers.The horizontal lines and node points illustrated in FIG. 5 represent thespan of each coil and the slots in which the coil sides or legs aredisposed. Thus, for group A1, a first coil extends from slot 1 to slot18, a second coil extends from slot 2 to slot 17, a third coil extendsfrom slot 3 to slot 16, and a fourth coil extends from slot 4 to slot15. It should be noted that these particular coils correspond to coils66, 68, 70 and 72, respectively of FIG. 4. Similar illustrations areprovided for all three phase A, B, and C, with numbers following thephase indication providing an identification of the coil group withinthe phase. As also illustrated in FIG. 5, certain coils will bepositioned singularly within slots, as indicated by reference numeral74. Other coils will share slots, as indicated by reference numeral 76.For the sake of clarity, rectangles have been shown in FIG. 5surrounding coils that share slots within the stator core.

The coils illustrated in FIGS. 4 and 5 are installed such that leads ofthe coil exit opposite ends of the stator core. In particular, in theillustration of FIG. 5, layers or sets of coils are installed asindicated by reference numerals 78, 80, 82 and 84. In a presentembodiment, sets 78 and 82 have leads that exit a first end of thestator core, while sets 80 and 84 have leads that exit an opposite end.As described more fully below, by installing sets 78 and 82 prior tosets 80 and 84, coils that share slots may be disposed within theirrespective slots, such that coils disposed within the base positions ofthe slots are fully installed prior to installation of coils disposedwithin a top position of the slots. Thus, in the illustration of FIG. 5,coils of group A1, installed with set 78, include coils disposed withinslots 3 and 4. These coils will be installed within the base of theircorresponding slots, and at base positions within slots 15 and 16. Uponinstallation of set 80, coils of groups B2 and C2 will be disposed intop positions over these coils, as indicated by the rectangles for slots3 and 4, and slots 15 and 16. Thus, sets 78 and 82 can be fullyinstalled in the core, followed by full installation of sets 80 and 84to provide the winding pattern illustrated in FIG. 5.

This exemplary winding pattern for this exemplary embodiment, by group,may be summarized as indicated in Table 1 below:

TABLE 1 Winding spans Lead exit Winding Slot span end A1  1-18 1 B125-42 1 C1 49-66 1 A2 37-54 2 B2 61-6  2 C2 13-30 2 A3 19-36 1 B3 43-601 C3 67-12 1 A4 55-72 2 B4  7-24 2 C4 31-48 2

The exemplary winding pattern, by individual coil, may be summarized asindicated in Table 2 below:

TABLE 2 Slot/winding distribution Slot Winding(s) 1 Ala 2 Alb 3 Alc/B2d4 Ald/B2c 5 B2b 6 B2a 7 B4a 8 B4b 9 C3d/B4c 10 C3c/B4d 11 C3b 12 C3a 13C2a 14 C2b 15 Ald/C2c 16 Alc/C2d 17 Alb 18 Ala 19 A3a 20 A3b 21 A3c/B4d22 A3d/B4c 23 B4b 24 B4a 25 Bla 26 Blb 27 Blc/C2d 28 Bld/C2c 29 C2b 30C2a 31 C4a 32 C4b 33 A3d/C4c 34 A3d/C4d 35 A3b 36 A3a 37 A2a 38 A2b 39Bld/A2c 40 Blc/A2d 41 Blb 42 Bla 43 B3a 44 B3b 45 B3c/C4d 46 B3d/C4c 47C4b 48 C4a 49 Cla 50 Clb 51 Clc/A2d 52 Cld/A2c 53 A2b 54 A2a 55 A4a 56A4b 57 B3d/A4c 58 B3c/A4d 59 B3b 60 B3a 61 B2a 62 B2b 63 Cld/B2c 64Clc/B2d 65 Clb 66 Cla 67 C3a 68 C3b 69 C3c/A4d 70 C3d/A4c 71 A4b 72 A4a

As will be appreciated by those skilled in the art, the number anddisposition of the windings within the stator may vary depending uponthe number of slots provided. For example, where fewer than 72 slots areprovided, the individual groups may have fewer than four windings. Wheresuch is the case, for example, in a stator having 60 slots, only asingle coil in each group may be disposed in a shared slot. For statorcores having still fewer slots, such as cores having 36 slots, thegroups may consist of only two coils, with a single coil being disposedin a shared slot and a coil being singularly located in a slot. Otheradaptations in accordance with the present technique may be envisaged.

FIG. 6 represents steps in an exemplary process for installing coils ina stator of the type described above. This process, indicated generallyby reference numeral 100, begins at step 102 wherein the coils orwindings are formed. As discussed above, the coils may be formed of asingle bar of conductive material, or may include multiple wraps ofwire, or bundles of wire. Following formation of the coils, the statorcore is mounted in an insertion station, as indicated at step 104. Theinsertion station maintains the core in a centralized position, andmakes one end of the core accessible to an insertion tool. At step 106,a first set of coils is inserted into the core through a first end ofthe core.

The steps of FIG. 6 are illustrated diagrammatically in FIG. 7. As shownin FIG. 7, at step 106, the core 26, being held in an insertion station,is processed such that a first set of coil groups 78 (see, e.g., FIG. 5)is inserted through a first end 28 of the stator core. The insertion, asindicated at arrow 122 of FIG. 7, disposes all of the coils of the firstset in their appropriate slots as described above. At step 108 of theprocess of FIG. 6, the stator core is rotated within the insertionstation. Referring again to FIG. 7, following insertion of the coilgroup set 78, the core is turned as indicated by arrow 126. The core ispreferably turned about a central vertical axis 124 such that there isno offset between the end 28 of the core and end 30 which is accessiblefollowing rotation of the core. At step 110 of the process of FIG. 6,then, a second set of coil groups is inserted through the second end ofthe core. In a diagrammatical representation of FIG. 7, arrow 128represents insertion of set 80 which includes coils and groupsillustrated diagrammatically in FIG. 5. As discussed above withreference to FIG. 5, the sets 80 inserted through end 30, in a presentembodiment, partially overlie the coils of set 78 inserted previouslythrough end 28. That is, certain of the coils of set 80 share slots andoverly certain coils of set 78.

At step 112 in the process of FIG. 6, the stator core is again rotatedin the insertion station. Again, this rotation, indicated by arrow 130in FIG. 7, preferably occurs about the central horizontal axis 124 ofthe stator core so as to avoid offset between the ends of the statorcore within the insertion station. Returning to FIG. 6, at step 114 thethird set of coil groups is then inserted through the first end of thestator core. As shown in FIG. 7, and as indicated at arrow 138, thethird set 82 of coil groups is inserted through end 28 such that theleads for these coils exits end 28, as do the leads for the set 78inserted previously. At step 116 of FIG. 6, the stator core is againrotated in the insertion station, and at step 118 the fourth set of coilgroups is inserted through the second end. As shown in FIG. 7, and asindicated at arrow 134, this rotation preferably occurs again about thecentral vertical axis 124, and the fourth set of coil groups 84 isinserted through the second end 30 as indicated by arrow 136. At thisstage in the processing, leads for sets 78 and 82 of coil groups exitend 28 of the stator core, while leads for sets 80 and 84 of coil groupsexit end 30 of the stator core. Following insertion of the fourth set ofcoil groups, the stator core is removed from the insertion station andfurther processed as indicated at step 120. As will be appreciated bythose skilled in the art, such further processing would generallyinvolve linking the coils into electrical groups, and terminating thecoils. The stator is generally further processed by applying aninsulating material, such as an acrylic resin, to the coils and core.Following final assembly of the stator, the stator is assembled in themotor housing with the remaining components of the motor in aconventional manner.

Various adaptations and modifications of the foregoing process may beenvisaged. For example, as shown in FIG. 8, in an alternativeprocessing, the coil group sets inserted by repeated rotation of thecore are inserted in two steps only. This process, identified generallyby reference numeral 140, begins at step 142 where, again, the coils arefirst formed. At step 144, the stator core is mounted in an insertionstation as in the preceding example. Referring to FIG. 9, in adiagrammatical representation, the stator core 26 is mounted in theinsertion station such that a first end 28 is accessible to an insertiontool. At step 146 of FIG. 8, the first and third coil group sets areinserted through this first end of the stator core. As shown in FIG. 9,the sets 78 and 82 are inserted through end 28 as indicated at arrow154. As noted above, the pattern of the coils and groups in accordancewith the present technique facilitates insertion of both sets 78 and 82without concern for overlying or underlying windings. That is, any coilsof sets 78 and 82 which share slots may be inserted such that thewindings lie in the base of their respective slots.

As indicated at step 148 in FIG. 8, the following insertion of the firstand third sets of coil groups, the stator core is rotated in theinsertion station. This rotation is indicated by arrow 156 in FIG. 9. Asin the previous example, the rotation preferably occurs about a centralvertical axis of the stator core to avoid offset between the ends of thecore in the insertion station. At step 150 of FIG. 8, the second andfourth sets of coil groups are inserted through the second end of thestator core. As shown in FIG. 9, and as indicated at arrow 158, in thisstep sets 80 and 84 are insert through end 30 of the stator core. Again,by virtue of the winding pattern offered by the present technique, anycoils of groups 80 and 84 sharing slots with coils of groups 78 and 82may be fully inserted, as the former only overlie coils in shared slotsof the previously inserted sets. Following insertion of the second andfourth sets of coil groups, the stator may be removed and furtherprocessed as indicated at step 152 in FIG. 8.

Where desired, further modification of the winding installation processmay be implemented as indicated diagrammatically in FIG. 10. In thisfurther modification, the stator core is mounted in an insertion stationwith ends 28 and 30 being accessible to different insertion tools or toan insertion tool which is capable of moving between the ends. Coilgroup sets 78 and 82 are then inserted through the first end 28 of thestator core as indicated by arrow 160 in FIG. 10. Again, all coils ofthese sets may be fully inserted as none of the coils underlie oroverlie one another in their respective slots. Subsequently, coils ofsets 80 and 84 may be inserted through end 30 as indicated by arrow 162in FIG. 10. Again, any coils of sets 80 and 84 which share slots withcoils of sets 78 and 82 will simply overlie those coils which havepreviously been inserted and installed in their respective slots.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A method for making a stator, the method comprising: installing afirst set of concentric coil groups through a first end of a statorcore, whereby leads of the first set of concentric coils exit the firstend of the stator core; installing a second set of concentric coilgroups through a second end of the stator core, whereby leads of thesecond set of concentric coils exit the second end of the stator core;installing a third set of concentric coil groups through the first endof the stator core, whereby leads of the third set of concentric coilsexit the first end of the stator core; and installing a fourth set ofconcentric coil groups through the second end of the stator core,whereby leads of the fourth set of concentric coils exit the second endof the stator core.
 2. The method of claim 1, wherein at least one coilof the third set of concentric coil groups is installed over a coil ofthe first set of concentric coils in a slot of the stator core.
 3. Themethod of claim 2, wherein at least one coil of the fourth set ofconcentric coil groups is installed over a coil of the second set ofconcentric coils in a slot of the stator core.
 4. The method of claim 1,wherein at least one coil of each coil group is installed in arespective stator slot with a coil of a different coil group.
 5. Themethod of claim 4, wherein at least one coil of each coil group isinstalled singularly in a respective stator slot.
 6. The method of claim1, wherein the coil groups define a four-pole, three-phase stator. 7.The method of claim 1, wherein the coil groups are disposed in an orderof A1, B4, C2, A3, B1, C4, A2, B3, C1, A4, B2, and C3, where A, B and Crepresent alternating current phases, and 1, 2, 3 and 4 represent coilgroups of the first, second, third and fourth sets, respectively.
 8. Themethod of claim 7, wherein the stator core includes 72 slots and eachcoil group includes 4 coils.
 9. The method of claim 1, wherein the coilgroups are installed in accordance with the following distribution: 1Ala 2 Alb 3 Alc/B2d 4 Ald/B2c 5 B2b 6 B2a 7 B4a 8 B4b 9 C3d/B4c 10C3c/B4d 11 C3b 12 C3a 13 C2a 14 C2b 15 Ald/C2c 16 Alc/C2d 17 Alb 18 Ala19 A3a 20 A3b 21 A3c/B4d 22 A3d/B4c 23 B4b 24 B4a 25 Bla 26 Blb 27Blc/C2d 28 Bld/C2c 29 C2b 30 C2a 31 C4a 32 C4b 33 A3d/C4c 34 A3d/C4d 35A3b 36 A3a 37 A2a 38 A2b 39 Bld/A2c 40 Blc/A2d 41 Blb 42 Bla 43 B3a 44B3b 45 B3c/C4d 46 B3d/C4c 47 C4b 48 C4a 49 Cla 50 Clb 51 Clc/A2d 52Cld/A2c 53 A2b 54 A2a 55 A4a 56 A4b 57 B3d/A4c 58 B3c/A4d 59 B3b 60 B3a61 B2a 62 B2b 63 Cld/B2c 64 Clc/B2d 65 Clb 66 Cla 67 C3a 68 C3b 69C3c/A4d 70 C3d/A4c 71 A4b 72 A4a,

wherein upper case letters A, B, and C indicate respective phases,digits 1, 2, 3 and 4 represent coil groups, and lower case leters a, b,c and d represent individual coils of each group.
 10. The method ofclaim 1, wherein the stator core is rotated between each installationstep.
 11. A method for making a four-pole, three-phase stator, themethod comprising: installing a first set of concentric coil groupsthrough a first end of a stator core, whereby leads of the first set ofconcentric coils exit the first end of the stator core; rotating thestator core; installing a second set of concentric coil groups through asecond end of the stator core, whereby leads of the second set ofconcentric coils exit the second end of the stator core; rotating thestator core; installing a third set of concentric coil groups throughthe first end of the stator core, whereby leads of the third set ofconcentric coils exit the first end of the stator core; rotating thestator core; and installing a fourth set of concentric coil groupsthrough the second end of the stator core, whereby leads of the fourthset of concentric coils exit the second end of the stator core.
 12. Themethod of claim 11, wherein the stator core is rotated about a centralvertical axis.
 13. The method of claim 11, wherein at least one coil ofeach group of the second coil group set is installed over a coil of agroup of the first coil group set in a respective slot of the statorcore.
 14. The method of claim 13, wherein at least one coil of eachgroup of the fourth coil group set is installed over a coil of a groupof the third coil group set in a respective slot of the stator core. 15.The method of claim 11, wherein at least one coil of each group isinstalled singularly within a respective slot of the stator core. 16.The method of claim 11, wherein the coil groups are disposed in an orderof A1, B4, C2, A3, B1, C4, A2, B3, C1, A4, B2, and C3, where A, B and Crepresent alternating current phases, and 1, 2, 3 and 4 represent coilgroups of the first, second, third and fourth sets, respectively. 17.The method of claim 11, wherein the stator core includes 72 slots andeach coil group includes 4 coils.
 18. The method of claim 11, whereinthe coil groups are installed in accordance with the followingdistribution: 1 Ala 2 Alb 3 Alc/B2d 4 Ald/B2c 5 B2b 6 B2a 7 B4a 8 B4b 9C3d/B4c 10 C3c/B4d 11 C3b 12 C3a 13 C2a 14 C2b 15 Ald/C2c 16 Alc/C2d 17Alb 18 Ala 19 A3a 20 A3b 21 A3c/B4d 22 A3d/B4c 23 B4b 24 B4a 25 Bla 26Blb 27 Blc/C2d 28 Bld/C2c 29 C2b 30 C2a 31 C4a 32 C4b 33 A3d/C4c 34A3d/C4d 35 A3b 36 A3a 37 A2a 38 A2b 39 Bld/A2c 40 Blc/A2d 41 Blb 42 Bla43 B3a 44 B3b 45 B3c/C4d 46 B3d/C4c 47 C4b 48 C4a 49 Cla 50 Clb 51Clc/A2d 52 Cld/A2c 53 A2b 54 A2a 55 A4a 56 A4b 57 B3d/A4c 58 B3c/A4d 59B3b 60 B3a 61 B2a 62 B2b 63 Cld/B2c 64 Clc/B2d 65 Clb 66 Cla 67 C3a 68C3b 69 C3c/A4d 70 C3d/A4c 71 A4b 72 A4a,

wherein upper case letters A, B, and C indicate respective phases,digits 1, 2, 3 and 4 represent coil groups, and lower case letters a, b,c and d represent individual coils of each group.